Before diving into NFC protocols, it pays to understand where NFC sits in the broader RFID landscape. RFID is not a single technology — it is a family of technologies that share the same fundamental principle (radio-frequency identification) but differ dramatically in frequency, range, data rate, cost, and application domain.
This chapter surveys that landscape from low-frequency animal trackers to ultra-high-frequency supply chain labels. Understanding the tradeoffs at each frequency will make the HF/NFC choices in later chapters immediately intuitive.
A passive RFID tag has no battery. It harvests the energy it needs to operate from the reader’s radio-frequency field. How that energy transfer works — and how data is exchanged — depends on whether the tag is in the near field or the far field of the reader antenna.
When the distance between reader and tag is much smaller than the wavelength of the carrier frequency, the dominant interaction is magnetic induction — the same principle as a transformer. The reader coil generates an alternating magnetic field; the tag coil picks up that field, rectifies it, and uses it as a power supply.
Data from reader to tag is encoded by modulating the amplitude of the reader’s carrier signal (ASK — Amplitude Shift Keying). Data from tag to reader is sent by load modulation: the tag switches a small resistance in and out of its coil circuit, which changes the load seen by the reader antenna and creates a detectable amplitude variation in the reader’s own signal.
Near-field coupling dominates at LF (125 kHz) and HF (13.56 MHz). The wavelengths are long (2.4 km at 125 kHz, 22 m at 13.56 MHz), so even at a few tens of centimetres the tag is well within the near field.
At UHF (860–960 MHz) the wavelength is around 33 cm. At reader-to-tag distances typical for supply chain use (1–10 m) the tag is in the far field, and inductive coupling is negligible. Instead, the reader illuminates the tag with a propagating radio wave. The tag harvests a small amount of power from this wave. It sends data back by switching the impedance of its antenna between two states — one that absorbs the wave and one that reflects it — producing a detectable change in the backscattered signal at the reader. This is called backscatter modulation.
Backscatter is more efficient at longer range because the power falls off with distance squared (propagating wave) rather than with distance cubed or sixth (near-field induction). However, the physics also makes UHF tags sensitive to the environment: liquids and metals detune antennas significantly.
| Band | Frequency | Wavelength | Coupling | Typical Range | Data Rate |
|---|---|---|---|---|---|
| LF | 125–134 kHz | ~2.4 km | Inductive | < 10 cm | 1–10 kbps |
| HF | 13.56 MHz | ~22 m | Inductive | < 10 cm – 1 m | 106–848 kbps |
| UHF | 860–960 MHz | ~33 cm | Backscatter | 1–10 m (passive) | 40–640 kbps |
| Microwave | 2.45 / 5.8 GHz | ~5 cm | Backscatter | Up to 1 m | varies |
| Standard / Chip | Notes |
|---|---|
| ISO 11784 / 11785 | Animal identification (FDX-B, HDX encoding) |
| EM4100 / EM4200 | Simple read-only ID cards; very widely deployed in legacy access control |
| HID Prox (HID 125 kHz) | Proprietary; dominant in North American building access |
| T5577 (ATA5577) | Writable LF chip; clones EM4100, HID Prox, and others |
Animal tagging. ISO 11784/11785 at 134.2 kHz is the international standard for livestock and pet microchips. The tag is encapsulated in glass, injected under the skin, and is expected to last the animal’s lifetime. The reader is a handheld wand or a walk-through frame.
Legacy access control. Millions of buildings worldwide still use EM4100-compatible cards and HID Prox readers. These are read-only, contain a fixed 40-bit ID code, and have no security — the ID can be read and cloned trivially. They persist because replacing installed infrastructure is expensive.
Industrial sensing. Some LF RFID chips include temperature or pressure sensors. The inductive coupling method works reliably through metal enclosures and fluid-filled pipes.
Immovable assets. LF tags are sometimes embedded in concrete, metal containers, or wooden pallets where the robustness to environment matters more than data capacity.
| Standard | Chip Examples | Notes |
|---|---|---|
| ISO 14443 Type A | MIFARE Classic, MIFARE Ultralight, NTAG, DESFire | Most common NFC subset |
| ISO 14443 Type B | ST25 (STMicro), some banking cards | Same frequency, different modulation |
| ISO 15693 | ICODE SLI, Tag-IT | “Vicinity” — longer range |
| ISO 18000-3 | Various | Generic HF RFID industrial |
This is the band where NFC lives. Chapters 2 through 6 focus entirely on this frequency.
Public transit. MIFARE Classic 1K is the dominant chip in transit cards worldwide. MIFARE DESFire EV2/EV3 is increasingly used for new deployments where cryptographic security is required.
Building and campus access. MIFARE Classic (legacy), DESFire (modern), and HID iCLASS (proprietary HF) are the main technologies.
Contactless payment. ISO 14443 is the physical layer for EMV contactless (Visa payWave, Mastercard Contactless) and mobile payment via NFC-enabled smartphones.
NFC-enabled smartphones. All modern smartphones include an NFC controller operating at 13.56 MHz. They can act as card readers (reader/writer mode), emulate contactless cards (card emulation mode), or exchange data with other NFC devices (peer-to-peer mode).
Library management. ISO 15693 (typically ICODE) is standard in public libraries because the longer range makes scanning a shelf of books practical without touching each one.
Healthcare. Patient identification bands, medication authentication, and device tracking.
Consumer NFC stickers. NTAG213/215/216 chips — which are ISO 14443 Type A compliant — are sold in the form of adhesive stickers for embedding in products, packaging, and smart home triggers.
| Standard | Notes |
|---|---|
| EPC Gen2 (ISO 18000-6C) | The dominant UHF standard; basis for GS1 EPC |
| ISO 18000-6A/B | Earlier, less common variants |
EPC Gen2 defines a 96-bit Electronic Product Code (EPC) that encodes company, product, and serial number — essentially a global barcode replacement.
Retail inventory. UHF RFID is deployed in apparel retail (Zara, H&M, Walmart mandates) for automated inventory counting. A reader can count thousands of items per second at several meters range.
Supply chain and logistics. Pallets and cases are tagged for automated tracking through warehouses and distribution centres. ISO 18000-6C / GS1 EPC is the standard.
Toll collection. Electronic toll systems (E-ZPass in the US, various European systems) use UHF at medium range.
Asset tracking. Large organisations use UHF for tools, equipment, and IT assets — a reader at a doorway can log every tagged item entering or leaving a room.
Aviation. The aerospace industry uses UHF RFID (ATA Spec 2000) for baggage tracking and aircraft component traceability.
Microwave RFID is less common but worth mentioning. At 2.45 GHz:
This band is not relevant for NFC work and is not covered further in this book.
When designing an RFID system from scratch, the frequency choice is the first and most consequential decision:
| Need | Recommended Band |
|---|---|
| Tag embedded in animal tissue / concrete | LF |
| Legacy compatibility with EM4100 / HID Prox | LF |
| Secure contactless smart card | HF (ISO 14443) |
| NFC smartphone interaction | HF (ISO 14443) |
| Library book tracking, shelf reading | HF (ISO 15693) |
| Long-range (> 30 cm) with non-metallic items | UHF |
| Supply chain pallet / case tagging | UHF |
| Real-time location (RTLS) | 2.45 GHz active |
For the rest of this book, the focus is HF at 13.56 MHz — specifically the ISO 14443 ecosystem. This is the band where MIFARE chips operate, where NFC smartphones operate, and where most developer-accessible tooling exists.
A few terms appear throughout the rest of the book:
| ← Introduction | Table of Contents | Chapter 2: NFC Standards → |